<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>父级比例</title>
    <style>
        html{
            height: 100%;
        }
        body{
            height: 100%;
        }.box{
            background-color: pink;
            /* %是相对于父级的百分比 */
            width: 50%;
            height: 50%;
        }
    </style>
</head>
<body>
    <div class="box"></div>
</body>
</html>